(a) Two friends while flying kites from different locations, find the strings of their kites crossing each other. The strings can be represented by vectors $\vec{a} = 3\hat{i} + \hat{j} + 2\hat{k}$ and $\vec{b} = 2\hat{i} - 2\hat{j} + 4\hat{k}$. Determine the angle formed between the kite strings. Assume there is no slack in the strings. OR (b) Find a vector of magnitude 21 units in the direction opposite to that of $\vec{AB}$ where A and B are the points A(2, 1, 3) and B(8, -1, 0) respectively.